In cellular phones, it is usual to employ a first circuit arrangement for driving light-emitting diodes and a separate, second circuit arrangement for polling a keypad. A multitude of terminal lines is required in each case for connecting the first circuit arrangement to the light-emitting diode and connecting the second circuit arrangement to the keypad.
The document “AS3688 Flexible Lighting Management (Charge Pump, DCDC Step Up, Current Sink, ADC, LDO)”, austria-microsystems AG, Preliminary Product Brief, describes a circuit arrangement wherein several light-emitting diodes are operated.
The document US 2006/0284741 A1 sets forth a keypad and an associated evaluation circuit.
The document U.S. Pat. No. 7,042,341 B2 deals with a circuit arrangement for polling a keypad and for operating a light-emitting diode as background lighting of the keypad.